The turbine section of a gas turbine engine is located downstream of a combustor section and contains a rotor shaft and one or more turbine stages, each having a turbine disk (rotor) mounted or otherwise carried by the shaft and turbine blades mounted to and radially extending from the periphery of the disk. Components within the combustor and turbine sections are often formed of superalloy materials to provide acceptable mechanical properties while at elevated temperatures resulting from the hot combustion gases. Higher compressor exit temperatures in modern high pressure ratio gas turbine engines can also necessitate the use of high performance nickel superalloys for compressor disks, bladed disks, and other components. Suitable alloy compositions and microstructures for a given component depend on the particular temperatures, stresses, and other conditions to which the component is subjected.
For example, airfoil components such as blades and vanes are often formed of equiaxed, directionally solidified (DS), or single crystal (SX) superalloys. Directionally solidified (DS) or single-crystal (SX) turbine airfoils have far superior creep strength, thermal fatigue resistance as well as corrosion resistance when compared to equiaxed crystal counterparts. In particular uses, DS or SX turbine airfoils have proven to have as much as nine times more relative life in terms of creep strength and thermal fatigue resistance and over three times more relative life for corrosion resistance, when compared to equiaxed crystal counter parts.
However, single crystal casting is a slow and expensive process. In the event of a change in design, a new mold has to be fabricated. Due to high melting temperature of the Nickel superalloy, often expensive ceramic molds are required. On the other hand, digital manufacturing methods, if successfully applied, can make a single crystal without a mold and thus enable design change economic.